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Use the environment variable "PRRT_CORES" to restrict a PRRT socket to
specific cpu cores.

- Use the much faster MPSC_queue algorithm to implement the pipe
- Replace the MPSC_queue by the propper pipe abstraction instead

It is possible that the timeout value overflows, and then, the 'now'
timestamp is always larger than the packet timeout. We need a proper
timeout detection.

- add debug domains which enable multiple debugging statements
  collectively
- add a debug domain DEBUG_ALL which enables all debugging messages
- print the debug domain in the debug message
- add some debug statements
- enable some domains

To print the domain, the debug() macro converts the domain into a
string and adds the value 6 to skip the "DEBUG_" prefix.

 - Implement PrrtTimestamp data structures and functions
 - Add PrrtTimeStampClock and PrrtTimeStampCycle macros where desired
 - Dump timestamp results to stdout